Use of fluorescence to monitor hydrophobic contaminants in a papermaking process

ABSTRACT

A method of monitoring and controlling one or more types of hydrophobic contaminants in a papermaking process is disclosed. The methodology utilizes the measurement of dyes, which are capable of fluorescing and interacting with the hydrophobic contaminants.

FIELD OF THE INVENTION

This invention pertains to the measurement and control of hydrophobic contaminants.

BACKGROUND OF THE INVENTION

Hydrophobic/organic contaminants, such as natural pitch, stickies, tackies and white pitch are major obstacles in paper manufacturing because these materials when liberated during a papermaking process can become both undesirable components of papermaking furnishes and troublesome to the mill equipment by preventing proper operation of mechanical parts when these materials deposit.

Increased use of secondary fiber, coated broke and mechanical pulp in the papermaking process contributes to the accumulation of organic contaminants. These contaminants can form deposits that affect machine runability and final product quality. Control of the contaminants is typically managed through chemical fixation, and its effectiveness is therefore dependent on the ability to determine the proper program and application. Historically, a common method used to assess program performance has been filtrate turbidity reduction. This method, however, is not entirely adequate because it often yields an incomplete picture of the furnish demands from hydrophobic particles. More recently, flow cytometry has been used in the industry for monitoring hydrophobic contaminants. Disadvantages of this method are that it is both labor and capital intensive.

A rapid and accurate method of measuring organic contaminants is therefore desired. Chemical control programs are often used to passivate or remove deposit-forming contaminants. For that reason, a method of screening the efficacy of chemical treatments that reduce the overall content of hydrophobic contaminants in a papermaking process is also desired.

SUMMARY OF THE INVENTION

The present invention provides for a method of monitoring one or more types of hydrophobic contaminants in a papermaking process comprising: (a) obtaining a bulk sample of fluid from said papermaking process; (b) selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; (c) adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; (d) measuring the fluorescence of the dye in said fluid; (e) correlating the fluorescence of the dye with the concentration of said contaminants; and (f) optionally controlling the amount of one or more chemicals that reduce or inactivate said contaminants which are added to said papermaking process.

The present invention also provides for a method for measuring the effectiveness of one or more chemicals that decrease the amount of one or more hydrophobic contaminants in a papermaking process: (a) monitoring one or more types of contaminants in a papermaking process comprising: obtaining a bulk sample of fluid from said papermaking process; selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; measuring the fluorescence of the dye in said fluid; and correlating the fluorescence of the dye with the concentration of said contaminants; (b) adding one or more chemicals to said papermaking process that decrease the amount of said hydrophobic contaminants; and (c) re-measuring the amount of contaminants in said papermaking process by performing step (a) at least one more time; and (d) optionally controlling the amount of said chemicals that are added to said papermaking process.

The present invention also provides for a method of monitoring one or more types of hydrophobic contaminants in a papermaking process consisting essentially of: (a) obtaining a bulk sample of fluid from said papermaking process; (b) selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; (c) adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; (d) measuring the fluorescence of the dye in said fluid; (e) correlating the fluorescence of the dye with the concentration of said contaminants; and (f) optionally controlling the amount of one or more chemicals that reduce or inactivate said contaminants which are added to said papermaking process.

DETAILED DESCRIPTION OF THE INVENTION

“Papermaking process” means a method of making any kind of paper products (e.g. paper, tissue, board, etc.) from pulp comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet and drying the sheet The steps of forming the papermaking furnish, draining and drying may be carried out in any manner generally known to those skilled in the art. The papermaking process may include a pulping stage, e.g. making pulp from woody raw material and bleaching stage, e.g. chemical treatment of the pulp for brightness improvement. Furnishes can contain fillers and/or other contaminants.

“Bulk sample” means a sample whose constituents have not been specifically separated, except bulk sample may include, a separation based upon size. For example, bulk sample does not include separating e.g. a resin particle from a suspension.

“Fluid” includes an aqueous papermaking suspension from a papermaking process, e.g. a fluid containing fibers in a pulping stage, a thin stock, a thick stock, aqueous suspensions drawn from the papermaking process, e.g. various locations from a papermaking machine or pulping process, aqueous fluid in a uhl box, press dewatering section, and/or any part of the papermaking process that one of ordinary skill in the art can think of where one would need to monitor hydrophobic contaminants.

As stated above, the present invention provides for a method of monitoring one or more types of hydrophobic contaminants in a papermaking process via the use of fluorescence.

The dyes, which are added to the sample must be able to stain or interact with the hydrophobic contaminants, e.g. pitch particles.

In another embodiment, the turbidity of the fluid is also measured. In a further embodiment, the turbidity of said fluid is measured before and after the addition of said chemicals.

In another embodiment, the fluid is filtered or diluted or a combination thereof prior to said addition of said dye or said fluorescent measurement of said dye, wherein said filtering or dilution of said fluid permits said fluid to be fluorometrically monitored.

In another embodiment, the sample is taken from a dilute sample point off a papermaking process, e.g. a paper machine. In a further embodiment, the sample point is the white water of a papermaking process. The reasoning postulated for this collection/sample point is that there is no long fiber present/substantially any fiber present, and filtration may not be necessary.

In another embodiment, one or more samples undergo a sieving/separation step to separate the long fiber from the suspended contaminants in a sample solution. For example, the degree of dilution that the filtrate/aqueous fraction undergoes from the separation process relies on two main factors, both relating to turbidity. If the filtrate/aqueous fraction is too turbid for the turbidimeter, dilution is required to bring the turbidity into a measurable range for the meter. This is the case unless you want a less accurate and “quick and dirty” test, which is one embodiment of the claimed invention.

In another embodiment, if the turbidity is above 2000 NTU (nephelometric turbidity units), then it is a preferred embodiment that a sample from a papermaking process is diluted/further separated prior to the addition of a dye and fluorescent measurement. The value of 2000 NTU may be instrument or measurement technique dependent.

In another embodiment, the fluid is an aqueous filtrate of a pulp slurry.

In another embodiment, the dye does not include N-(n-butyl)4-(n-butylamino)-naphthalimide.

In another embodiment, the fluid is obtained from a wet end of said papermaking process.

As stated above, the dye added to a sample must have a sufficient amount of time for said dye to interact with said contaminants in said fluid prior to its fluorescent measurement. One of ordinary skill in the art could determine a sufficient amount of time for said interaction without undue experimentation.

In one embodiment, the dye is mixed with a solvent prior to its addition to said fluid. One of ordinary skill in the art could determine an adequate time for mixing without undue experimentation.

In another embodiment, the contaminants are selected from the group consisting of: pitch, fiber, filler, fines, coated broke, mill broke, recycle, groundwood, thermal mechanical pulp, chemi-thermal mechanical pulp, chemical pulp, deinked pulp, ink, adhesives, stickies, tackies, waxes, binders and dissolved and/or colloidal substances, and a combination thereof.

In another embodiment, the method is an on-line method and/or batch sample method.

In another embodiment, the fluorometric measurement is performed at a pre-set basis, intermittent basis, and/or continuous basis. For example, a flow cell can be utilized as a means for measuring the fluorescence of said hydrophobic contaminants. More specifically, in one embodiment, a process for measurement comprises: the addition of one or more fluorescent tracers to a sample obtained from a papermaking process prior to its fluorescent measurement in said flow cell. One of ordinary skill in the art would be able to carry out this process without undue experimentation. For example, one could utilize flow injection analysis and/or sequence injection analysis techniques to carry out the above-referenced measurement protocol.

In another embodiment, the fluorometric measurement is performed with a handheld fluorometer. A fluorescent measurement may be carried out with other types of fluorometers.

The present invention also provides for a method of measuring the effectiveness of one or more chemicals that decrease the amount of one or more hydrophobic contaminants in a papermaking process. The information on the amount of hydrophobic contaminants in a fluid can be utilized to form a control loop for the addition of one or more chemicals, which can be used to control the amount of hydrophobic contaminants.

In one embodiment, the methodology for monitoring the hydrophobic contaminants can be measured by the above-stated fluorescence methodology and its various embodiments.

In another embodiment, a determination of the amount of fluorescence is measured by the above-mentioned protocol, then subsequent to this step, an addition of one or more chemicals to the papermaking process to treat the hydrophobic contaminants, e.g. increase/decrease in the same chemistry for hydrophobic contaminant inhibition or change in the chemistry treatment program for hydrophobic contaminant inhibition, and then subsequent to the treatment step, a re-measurement of the amount of contaminants in said papermaking process by the above-mentioned protocol.

In another embodiment, the chemicals are at least one of the following: a fixative; a detackifier; a dispersant; a surfactant; and a retention aid. 

1. A method of monitoring one or more types of hydrophobic contaminants in a papermaking process comprising: a. obtaining a bulk sample of fluid from said papermaking process; b. selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; c. adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; d. measuring the fluorescence of the dye in said fluid; e. correlating the fluorescence of the dye with the concentration of said contaminants; and f. optionally controlling the amount of one or more chemicals that reduce or inactivate said contaminants which are added to said papermaking process.
 2. The method of claim 1 further comprising: measuring the turbidity of said fluid.
 3. The method of claim 2 wherein said turbidity of said fluid is measured before and after the addition said chemicals.
 4. The method of claim 1, wherein said fluid is filtered or diluted or a combination thereof prior to said addition of said dye or said fluorescent measurement of said dye.
 5. The method of claim 1, wherein said dye does not include N-(n-butyl)-4-(n-butylamino)-naphthalimide.
 6. The method of claim 1 wherein said fluid is obtained from a wet end of said papermaking process.
 7. The method of claim 1 wherein said dye is mixed with a solvent prior to its addition to said fluid.
 8. The method of claim 1, wherein said contaminants are selected from the group consisting of: pitch, fiber, filler, fines, coated broke, mill broke, recycle, groundwood, thermal mechanical pulp, deinked pulp furnish, chemi-thermal mechanical pulp, chemical pulp, ink, adhesives, stickies, tackies, waxes, binders and dissolved and/or colloidal substances, and a combination thereof.
 9. The method of claim 1, wherein said method is an on-line method and/or batch sample method.
 10. The method of claim 1, wherein said fluorometric measurement is performed at a pre-set basis, intermittent basis, and/or continuous basis.
 11. The method of claim 1, wherein said fluorometric measurement is performed with a handheld fluorometer.
 12. The method of claim 1, wherein said fluid is an aqueous filtrate of a pulp slurry.
 13. A method for measuring the effectiveness of one or more chemicals that decrease the amount of one or more hydrophobic contaminants in a papermaking process: a. monitoring one or more types of contaminants in a papermaking process comprising: obtaining a bulk sample of fluid from said papermaking process; selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; measuring the fluorescence of the dye in said fluid; and correlating the fluorescence of the dye with the concentration of said contaminants; b. adding one or more chemicals to said papermaking process that decrease the amount of said hydrophobic contaminants; and c. re-measuring the amount of contaminants in said papermaking process by performing step (a) at least one more time; and d. optionally controlling the amount of said chemicals that are added to said papermaking process.
 14. The method of claim 13, wherein said chemicals are at least one of the following: a fixative; a detackifier; a dispersant; a surfactant; and a retention aid.
 15. A method of monitoring one or more types of hydrophobic contaminants in a papermaking process consisting essentially of: a. obtaining a bulk sample of fluid from said papermaking process; b. selecting a hydrophobic dye that is capable of interacting with said contaminants in said fluid and fluorescing in said fluid; c. adding said dye to said fluid and allowing a sufficient amount of time for said dye to interact with said contaminants in said fluid; d. measuring the fluorescence of the dye in said fluid; e. correlating the fluorescence of the dye with the concentration of said contaminants; and f. optionally controlling the amount of one or more chemicals that reduce or inactivate said contaminants which are added to said papermaking process. 